Abstract: Deformation damage due to excavation unloading is a common phenomenon.It was observed in the bottom of riverbed during the excavation of a hydropower station dam foundation in Southwest China.The depth and intension of excavation unloading and intension have become a key problem in dam construction and its longtime stability.The characteristics of deformation damage in dam foundation rock mass under condition of excavation unloading area are examined by using FLAC3D software.On the basis of the in-situ unloading fissure data,numerical analysis gives the affected depth and intensity of the riverbed dam foundation due to excavation unloading in the studied zone.This result can provide the necessary information for dam foundation integrative curing and can be use as reference data for the similar projects in the future.